In ordinary refrigerators, a refrigerant is repeatedly cycled alternately liquifying by condensation and gasifying by evaporation within a refrigeration circuit. A refrigerator will cool the surrounding area by removing heat therefrom when the refrigerant is gasified by evaporation. Refrigerators are commonly provided with a refrigerant compressor attached in the refrigeration circuit thereof, which compressor sucks the evaporated refrigerant for compressing the same before feeding it to a condenser.
If the refrigerant enclosed in the refrigeration circuit leaks by any chance outside the circuit to consequently reduce the amount of the refrigerant therein, there is a likelihood of taking place an overheating of the compressor due to deterioration of the cooling function thereof, and particularly in the event misty oil included in the refrigerant is expected to function as a lubricant the compressor will naturally be visited by a lubrication shortage through the refrigerant shortage, which often causes a seizure of the compressor.
It is therefore required to stop the operation of the compressor, in such a refrigerant leakage case down to a level below a certain predetermined limit, by means of sensing the amount of the refrigerant within the refrigeration circuit. Two ways of sensing such a refrigerant decrease (reduction) by a leakage have been known so far; one is to sense the refrigerant temperature, which is said to rise in response to the decrease of the refrigerant amount, and the other is to sense the temperature of the oil pan disposed in the bottom portion of the refrigerant compressor (hereinafter simply called a compressor) to detect the decrease of the refrigerant enclosed.
The two methods introduced above, i.e., variation of the refrigerant temperature or the oil pan temperature are not satisfactory in the capability of accurately responding to the decrease of the refrigerant. The seizure of the compressor has not been completely prevented due to the difficulty of accurately catching the information of the refrigerant reduction. Another disadvantage lies, in the refrigerant temperature measuring (sensing) method, in the difficulty of mounting the sensor within the structure of the compressor while severely keeping the gas-tightness between the two.